1. Field of the Invention
The present invention relates generally to an apparatus for manufacturing semiconductor chip packages, and more particularly to a die bonding apparatus having a multiple bonding system in which semiconductor chips are supplied one by one from a single wafer cassette and bonded to lead frames at more than one position.
2. Description of The Related Art
Generally, after a wafer fabrication process in which predetermined patterns of integrated circuits (IC) are formed on silicon wafers, the assembly process for semiconductor IC device packages begins. As illustrated in FIG. 1, the assembly process 1 generally consists of a wafer sawing step 11 in which a wafer is cut and divided into a plurality of dies, a die bonding step 12 in which an individual die (or chip) separated from the wafer is mechanically attached to a lead frame unit (one of several that are adjacently arranged along a lead frame strip), a wire bonding step 13 in which the dies are electrically coupled to the lead frame units by means of wires, a molding step 14 in which a package body is formed from a molding compound in order to protect the die, the wires, and connections from hostile environments, and a trimming and forming step 15 in which the individual packages are separated, the outer leads are trimmed, and the package is adapted for mounting on the circuit board.
In particular, the die bonding process 12 is further illustrated in FIG. 2. In wafer loading step 21 the wafer dies, which have already been sawed but remain arranged on a wafer, are supplied to a die bonder. The individual die is separated from the wafer and supplied to a bonding position in a die pickup & mount step 22. A lead frame strip is prepared with adhesive and placed at the bonding position in lead frame transfer step 23. In die bonding step 24 the die and a lead frame unit of the lead frame strip at the bonding position are attached to each other. In unloading step 25 the die-bonded lead frame strip is unloaded from the bonding position and made ready for loading into a wire bonder.
Various methods have been used for the die bonding step 24. These methods, using different adhesive materials, include gold-silicon eutectic die attach, polymer die attach, solid-film polymers die attach, and solder die attach.
The die bonding process 12 is conducted independently from the wire bonding process 13. This requires time, space and labor for the movement of the materials between die bonding process 12 and wire bonding process 13, causing low productivity. A single automated in-line system has recently been developed and proposed to overcome the drawback of the prior independent systems.
Such an automated in-line system is characterized as a single-bonding system. It includes one die bonder connected to more than one wire bonder by means of a transfer rail. Accordingly, the die-bonded lead frame strips can be directly and automatically supplied to the wire bonder. Since the time required for the wire bonding process 13 is longer than the time required for the die bonding process 12, it is possible to connect more than two wire bonders to each die bonder. In these conventional single-bonding systems, the number of wire bonders per die bonder ranges from two to six.
However, in the case of lead-on-chip (LOC) packages in which a solid-film polymer such as polyimide tape is used as a bonding material for attaching dies to a lead frame, the die bonding time required is longer than that for packages using other bonding materials. Accordingly, only one or two wire bonders are connected to one die bonder, which results in less of an advantage for the conventional single-bonding in-line systems.
A need exists, therefore, for a die bonding apparatus that provides more bonded lead frames per unit time, especially for LOC packages, to feed the plurality of wire bonders connected in an automated in-line system.